1. Field of the Invention
The present invention relates generally to microelectromechanical systems, and more particularly to methods and apparatuses for singulating dies containing a multiplicity of microelectromechanical systems (i.e., MEMS)
2. Description of the Related Art
Microelectromechanical systems are integrated micro devices or systems combining electrical and mechanical components fabricated in the similar processes to those used in the fabrication of standard integrated circuit devices. However, unlike standard integrated circuits which process electronic signals in either a digital, analog, or mixed digital/analog fashion, microelectromechanical systems are capable of and are functionally designed to generate electronic signals by their ability to undergo physical deformation or motion in response to external physical stimuli such as acceleration, external atmospheric pressure or temperature, and acoustic waves. Due to their small size and durable nature, microelectromechanical systems are capable of operation in environments that would otherwise be unsuitable for more conventional devices. Devices such as microminiature microphones, pressure gauges, accelerometers, strain gauges, bio-mechanical valves, actuators, and temperature transducers (some with critical dimensions approaching 50 microns) have become both technologically and economically feasible to produce in production quantities.
Microelectromechanical systems are fabricated in the same manner as more conventional integrated circuits using the same fabrication technology and processes. Prior to packaging, the wafer containing dies with completed microelectromechanical systems must be diced to singulate the individual dies. The standard singulation process requires a wafer saw or other methods known to those skilled in the art to physically cut the wafer along prescribed lines known in the art as "saw streets". Unfortunately, the cutting process generates a substantial amount of debris and excess thermal energy, either of which will adversely affect the number of functional dice available for final assembly. It is thus of paramount importance that this debris and excess thermal energy be removed during the dicing operation. Conventionally, a high pressure jet of water is used to clear the debris and act as lubricant as well as coolant for the wafer saw. Eventhough the high pressure jet of water effectively removes both the debris and excess thermal energy, it represents a source of damage to any structures on the surface of the wafer. Conventional methods for protecting these structures calls for the application of a substantially water insoluble protective layer covering the surface of the wafer and the microelectromechanical systems, thereon, prior to the actual sawing operation. Traditionally, this protective layer has been a substantially water insoluble photoresist which must be removed subsequent to the wafer saw operation so as to not adversely impact final assembly yield. A significant problem with use of photoresist or any other substantially water insoluble material as the protective layer is the requirement of a post saw clean operation using environmentally unfriendly solvents (i.e., acetone) to remove the protective layer from the surface of the wafer and associated microelectromechanical systems.
FIGS. 1A through 1D illustrate the conventional method of singulating dice containing microelectromechanical systems using a substantially water insoluble protective layer. FIG. 1A is a diagrammatic side view of a wafer 200 attached to a mounting tape 902 containing a plurality of dies 101 some of which have associated microelectromechanical systems 100 located on an upper surface 201 of the wafer 200 attached to mounting tape 902. The microelectromechanical systems 100 are fabricated utilizing the same or similar processes and materials as is used for fabrication of standard semiconductor circuits but are designed to generate electronic signals based upon the physical response of the structures to external physical stimuli such as pressure, temperature, acoustic waves, acceleration. FIG. 1B is a diagrammatic side view of wafer 200 attached to mounting tape 902 showing a conventional protective layer 120 covering the associated microelectromechanical systems 100. Conventional practice dictates protective layer 120 be composed of a substantially water insoluble material (such as photoresist) applied prior to the actual dicing operation. For example, a wafer saw (not shown) or any other method known in the art, scribes and cuts the wafer 200 attached to mounting tape 902 along prescribed lines well known in the art as "saw streets" 110 which delineate the boundaries of the individual dies 101. As illustrated in FIG. 1C, the wafer saw produces a die cut 130 with a depth, c, substantially cutting wafer 200 attached to mounting tape 902 leaving approximately a section of mounting tape 902 of thickness, d, as a support structure for subsequent cleaning and mounting operations performed on the singulated dies. Completion of the dicing operation requires protective layer 120 be substantially removed from the microelectromechanical systems 100 so as to not interfere with their designed function. FIG. 1D is a diagrammatic side view of wafer 200 attached to mounting tape 902 subsequent to removal of protective layer 120 but prior to final singulation of the individual dies 150 containing microelectromechanical systems 100. Unfortunately, as can be readily seen in FIG. 1D, a varying amount of substantially water insoluble protective layer 140 residue remains after the cleaning operation; the amount and location of which will ultimately determine the number of functional die available for final assembly.
In view of the foregoing, there is a need for methods and apparatuses that allow the dicing of wafers containing microelectromechanical systems into singulated individual dies that is economic to use and leaves substantially no residue on the surface of the individual dies.